Planetzymals (“embryos” of the planets) could not have been a source of water on Earth due to their extreme dryness. article about it published in nature.
Planetzymals are ancient bodies of the solar system that emerged from the protoplanetary disk. When the dust deposits reach a radius of about one kilometer, their movement is not affected by the gas resistance and they gradually begin to attract the surrounding matter. Thus, planetary emeralds grow larger and larger, and when they reach a radius of 1-3 kilometers, their rocks undergo metamorphism, melting and differentiation (like the bowels of the earth). According to one of the hypotheses, it was such minor planets that fell on the Earth and brought water to it.
Scientists from the University of Maryland analyzed the composition of seven achondrite meteorites that fell to Earth. These meteorites are thought to be planetary separations, as they show signs of strong compression and high temperatures. Some of the seven meteorites studied came from the dry interior of the solar system, while others formed in the outer part where stable ice could exist. These rocks turned out to be incredibly dry and contain no more than two million parts of water by mass.
“We knew that many objects in the outer solar system were differentiated, but it was assumed that they must contain a lot of water because they came from a part where ice could exist,” said Sune Nielsen, one of the authors. Study from the Woods Institution of Oceanography.-Hole. “Our work shows that this is certainly not the case. When minor planets melt, they are left without water.”
This means that neither the small planets that fell to Earth as meteorites nor the small asteroids that broke off from them could serve as a source of water. Only untransformed bodies could bring water to Earth, the exact composition of which has yet to be determined.